Abstract: The calibration factor is a parameter used to characterize the reading accuracy of RF power sensors, defined as the ratio of the power displayed by the sensor to the incident power. It is the object of power value transfer. This paper introduces the composition and measurement principles of the direct comparison method and the VNA-based direct comparison method. It describes the application of the equivalent source reflection coefficient in the direct calibration method. The calibration factor of the Rohde & Schwarz NRP50T power sensor was measured using both the direct calibration method and the VNA-based direct comparison method. Results show that the maximum difference between the corrected calibration factors measured by the two methods is 3.056%. The equivalent source reflection coefficient of the VNA-based direct comparison method is generally larger than that of the direct comparison method. The uncertainty evaluation method for the direct comparison method is well-established, making it currently the most prevalent RF power sensor calibration method.